Apparatus for electrophotographic printing



April 1962 D. F. KELLER ETAL 3,028,799

APPARATUS FOR ELECTROPHOTOGRAPHIC PRINTING Filed March 8, 1957 2Sheets-Sheet 1 Fag. Z

A ril 10, 1962 D F. KELLER ETAL 3,028,799

APPARATUS FOR ELECTROPHOTOGRAPHIC PRINTING Filed March 8, 1957 2Sheets-Sheet 2 United States atent ce 3,028,799 Patented Apr. I 10, 1962 3,028,799 APPARATUS FOR ELECTROPHOTOGRAPHIC PRINTING Daniel FranklinKeller, 525 Sheridan Road, Kenilworth, Ill., and Harry E. Gunning, HazelCrest, Ill., assiguors, by mesne assignments, to Daniel Franklin Keller,Kenilworth, Ill.

Filed Mar. 8, 1957, Ser. No. 644,754 16 Claims. (Cl. 951.7)

This application is a continuation-in-part of our copending applicationSerial No. 590,621, filed June 11, 1956, now US. PatentNo. 3,000,735issued September 19, 1961.

This invention relates generally to electrophotography andelectrophotograhic printing and, more particularly, to improved methodsand apparatus for producing latent charge images on surface meanssuitable for use in printing and reproduction procedures, for example,by electrophotographic means.

By exposing photoemissive or photoconductive layers or surfaces toradiation having a desired image or pattern, there is produced acorresponding emission of electrons in the areas receiving the radiationwhereupon an electrostatic latent image is produced. The electric chargepattern which forms the electrostatic latent image may be renderedvisible by various developing procedures, for example, by depositing asuitable material such as finely divided particles which come under theinfluence of the charge pattern.

In following the procedures outlined heretofore, it has been necessaryto utilize bulky equipment oftentimes necessitating the use of highvoltage generating equipment. Artisans in the field have been confrontedwith serious problems with respect to the uniformity of a chargingfield, the lack of flexibility with respect to the size of the imagesreproduced and the safety factors which are present in connection withthe high voltage equipment employed.

Further, methods heretofore used have not been adaptable to, utilizationin an apparatus of a size and weight and having simplicity to be used asa camera or to be used in a printing system. In accordance with theprinmanent image by electrophotographic means. The present inventionalso contemplates the provision of methods and apparatus which may beutilized in a relatively uncomplicated printing arrangement whereincopies or prints are rapidly and directly made from the permanent imagewith the utilization of electrophotographic processes.

In accordance with the principles of the present invention, it iscontemplated to provide as a charging means in an electrophotographicprocess a layer formed from an electrically stressed substance andproviding an eifective working surface which exhibits a permanentelectrostatic field as high as 30,000 volts per centimeter. A layeredmember so provided is sometimes referred to in the electrostatic arts asan electret.

A feature of the present invention is to provide a camera wherein thelight radiation passing through the lens falls upon a photoconductivestrip backed by an electret and wherein the strip is subsequently drawnthrough a dusting chamber and thereafter through a fixing chamber sothat the dust which is gathered upon the surface in the form of theimage will be permanently fixed to the strip of material.

It is another feature of the invention to provide a method and apparatusfor the printing of copies from permanent images by 'anelectrophotograpln'c process wherein a surface means bearing a permanentimage is placed against one surface of a transparent electret and lightradiation projected through the surface means and electret wherein alatent image is formed on a photoconductive coating on the oppositesurface of the electret. The image is rendered visible by applying adusting powder and this image is transferred by a surface having anafiinity for the powder and carried to an electret having a polarityopposed to the polarity of the first electret surface whereby the imagewill be attracted to a paper placedbetween the transfer surface and thesecond elec tret.

Another feature of the invention lies in the provision of a method andapparatus for utilization in a camera wherein a photoconductive layer isutilized as a surface bearing a latent charge image and succeedinglypassd over ends of an electret or" opposite polarity and thereafterpositioned against a grounding plate and exposed to radiation from animage and the image is subsequently fixed on the photoconductive surfaceby passing it through a dusting chamber. The surface bearing means issubsequently passed through a spray chamber wherein the a printingmethod and mechanism wherein a surface hearing an image is placedagainst a surface of an electret and a photosensitive insulatingmaterial on thin plastic is placed over the surface and exposed to alight and subsequently passed to a dust chamber.

The plastic material with the photoconductive insulating surface issubsequently exposed to another light and carried against a copymaterial held against an electret surface having an outer surface ofopposite polarity from the surface beneath the surface bearing the imagewhereby dust which has been placed on the surface of the plasticmaterial in accordance with the density of the image is transferred tothe copy material producing a printed copy of the image.

It is, therefore, an object of the present invention to provide anelectrophotographic method and apparatus wherein a strip of supportingmaterial coated with a photoconductive insulator may be fed through acamera to produce a latent charge image by an electrophotographicprocess conducted entirely within the camera.

Another object of the invention is to provide a mechanism wherein apermanent image is produced Within a camera by drawing a clear plasticfilm coated with a photoconductive insulating material over an electretand exposing the film to radiation and subsequently drawing the filmthrough a dust chamber and a spray chamber to develop and fix the film.

Another object of the invention is to provide a camera wherein a filmcoated with a photosensitive layer is sequentially drawn over surfacesof opposite polarity on the electret and thereafter placed against aground plate and exposed to the radiation of an image and substantiallydrawn through a dust chamber and spray chamber to develop and fix theimage on the film.

Another object of the invention is to provide an improved photoelectricprinting method and apparatus which is simple in construction andoperation and wherein copies or prints 'may be directly and continuouslymade by a photoelectric process obviating the necessity of providingexpensive and complex equipment such as has heretofore been necessary.

Another object of the invention is to provide an electrophotographicprinting process which finds utility in a printing mechanism wherein apowder deposited in the form of an image is carried by a transferblanket to a printing paper.

Another object is to provide another form of mecha- 3 nism wherein thepowder may be transferred directly to, a printing paper and fixedthereon.

Other objects and advantages will become more apparent in the teachingsof the principles and features of the invention with the disclosure ofthe preferred embodiments thereof in the specification, claims anddrawings, in which:

FIGURE 1 is a somewhat schematic vertical sectional view of one form ofa camera employing the principles of the invention;

FIGURE 2 is another vertical sectional view taken through the camera andshowing schematically another form of the camera;

FIGURE 3 is a vertical sectional view shown in schematic form of aprinting mechanism for making copies or prints of images; and

FIGURE 4 is avertical sectional view shown in schematic form of anotherarrangement of a printing mechamsm.

In the embodiments of FIGURES 1 and 2, the invention is shown using anelectret in a box or similar hand camera for purposes of makingpermanent images.

As used herein, the term electret denotes a permanent- 1y electrifiedsubstance exhibiting electrical charges of opposite sign at itsextremities and of the type disclosed in our acknowledged co-pendingapplication.

Electrets are made from solid substances which are capable of beingmelted without chemical decomposition and which possess a finite dipolemovement in liquid state, for example, carnauba wax-beeswax mixtures,mixtures of carnauba wax with various synthetic, thermoplastic or polarresin such as polyvinyl chloride polymers, etc., soda-lime glass, Pyrexglasses, quartz, and sulfur.

A permanent charge is imposed upon the substance of the electret byallowing the liquid electret-forming substance to solidify in a strongelectric field. For example, the substance may be melted whileinterposed between two electrically-independent tinfoil electrodesattached to opposite poles of a high voltage D.C. source furnishing aDC. field of not less than 10,000 volts per centimeter. The liquidsubstance is allowed to remain in the fluid state within the field forat least one hour and is, thereafter progressively cooled at a slow ratewithin the field until completely solidified.

It has been found that electrets so formed are permanentlyvolume-polarized and possess permanent electrostatic fields of oppositepolarities at the extremities or surfaces thereof to which theelectrodes were attached.

In the electrophotographic processes of the prior art, charges in therange of 4500 to 6000 volts per centimeter have been utilized, Thepermanent electrostatic fields possessed by electrets may range from afew hundred volts per centimeter and may exceed as high as 30,000 voltsper centimeter at the working surfaces of the electret and, accordingly,it is contemplated according to the principles of the present inventionthat the electret will be provided with surfaces exhibiting a permanentelectrostatic field in the order of magnitude of a few hundred volts toan upper limit determined by the breakdown potential of the air incontiguity to the charged surface.

Although the principles of the present invention find specific utilityin the embodiments illustrated and described, it will be understood thatthe features and advantages of the invention may be utilized in otherenvironments and the specific forms shown are for purposes 7 ofillustration and for purposes of disclosing the preferred forms.

As illustrated in FIGURE 1, a camera is illustrated as having a housingshown diagrammatically at 10 with a bellows 12 or similar lightproofenclosure defining a camera chamber 14. At the front of the camerachamber is a lens and shutter assembly 16 with lenses 18 and a shuttersystem 20. The lens and shutter arrangement are the type known to theart whereby the shutter system 20 maybe opened for a predeterminedperiod of time to permit the passage of light radiation through the lensin accordance with the reflective properties of the image to bephotographed.

At the focal point of the lens is a reflector plate 22 which is set at a45 angle with the camera shown in the horizontal position, so that theimage is reflected upwardly against a supporting surface adapted to havea latent charge image formed thereon, sometimes referred to herein as afilm 24.

The film may conveniently comprise a backing or carrying layer with alayer of photo-conductive material thereon such as sulfur, anthracene ormercuric sulfide. Means for supplying the film are shown in the form ofa supply roll 26 from which the film is threaded to be positionedagainst the ground plate 28 in the picture taking location. The end ofthe film next passes through a dusting chamber 38 and then passes into aspraying chamber 40.

The spraying chamber is provided with a hinged door 42 which may beswung open about its supporting hinge 4+4 to remove the developed andfixed end of the film at 46.

In advancing the film into the camera, the film is first drawn over ascanning bar or roller 48 positioned to be in engagement with the film.The scanning bar 48 is of a polarity determined by electret 50.

The electret member 50 comprises a body 52 with a first lower surace 54and a second upper surface 56. The surfaces 54 and 56 are spaced fromeach other and parallel and exhibit a permanent electrical charge withthe surfaces 54 and 56 being of opposed polarity in accordance with thedefinition of theterm electret.

As illustrated in FIGURE 1; the electret 50 is provided on the surface54 with an electrically conductive layer 58. The surface 56 is providedwith an electrically conductive layer 60.

Attached to the first electrically conductive layer 58 is an electricallead 61 which is electrically connected to the scanning bar 48 so as toplace a charge on the surface of the coated paper in accordance with theelectrostatic charge on the surface 54 of the electret.

As the film 24 is drawn forwardly to an image-forming location 62, itpasses over the electrically conductive sur-- is positioned injuxtaposed relationship to the ground plate 28.

The light-conducting film has been in location to receive lightradiations of the image. As the shutter system 2.0 is opened, the film24 is exposed to radiation and surface electrons are discharged to theground plate 28 in the shape and density of the image.

The film 24 is next rolled forward to pass through the dusting chamber38. The dusting chamber exposes the photoconductive surface to finepigment particles and these particles are picked up in the shape anddensity of the image.

Guide pins 41 or the like may be provided to guide the film as it passeswith its surfaces 43 exposed to the dusting chamber 38. The dustingchamber 38 may be provided with seals at its edges to avoid the escapeof dust down into the camera chamber 14 or up into the spray chamber 40.The dust may be created by agitation means or may be applied by a brushsimilar to an iron filing brush of the type known to the art.

After being developed, the dust coated film is drawn up into the spraychamber 40 where the image is fixed. The fixing is accomplished byapplying a spray such as by nozzle 64 which sprays over the surfaceofthe end of the image and causes a permanent adherence of the dust tothe film in the density and shape of the image. A plastic solution spraysuch as Krylon or any solid 3 plastic dissolved in a volatile solvent,which solvent is compatible with the film material, may be applied tofix the image.

In the form show in FIGURE 2, the camera is pro: vided with a housing 66having a lightproof bellows 6-8 forming a camera chamber 70. At thefront of the chamber is located a lens and shutter assembly 72 carryinglenses 74 with a shutter system 76. The assembly 72 is arranged so thatthe shutter may be opened for a predetermined length of time to permitlight radiation corresponding to the image to pass rearwardly within thecamera chamber 70. At the back of the camera in an image-forminglocation 78 is the film 80. The film may be a backing paper with aphotoconductive insulating material thereon and is preferably formed ofa roll of clear plastic with a photoconductive insulating surface.

The film is supplied from a supply roll 82 housed in an upper portion 84of the housing 66 and feeds downwardly to the image-forming location 78and subsequently through a dust chamber 86 and a spray or fixing chamber88.

In moving to the image-forming location 78, the film 80 passes .alateral ground brush 91. The ground brush may be moved across the faceof the film along the guide 93 or it may be more feasible to positionthe ground to contact the film as it comes off the roll 82 as a groundon the face of the electret may bring charges to the surface.

In the picture-taking location, the film is backed by an electret'90which is shown in the form of a flat plate 92 having opposed parallelsurfaces 94 and 96, which exhibit permanent electrostatic charges ofopposing polarity.

In the picture-taking location, the shutter system is opened whereuponthe film 80 is exposed to radiation. A latent electrostatic image isproduced on the film in the configuration and density of the image.

After the image has been formed on the film, it is rolled downwardly topass into the dusting chamber 86. In this chamber, the film is exposedto a finely separated pigment or dust which attaches itself to thesurface in the configuration and density of the image and changes thelatent electrostatic image to a visible image. The film portion 98,which is in the dust chamber 86, is guided by spaced horizontallyextending guiding bars 160'.

The leading end 102 of the film is rolled forwardly into the spray orfixing chamber 8-3. At this location a spray nozzle 104 is supplied froma manifold or container 106 and sprays a material such as a clearplastic coating to fix the powdered material to the surface of the filmend 102. The end 102 of the film upon which the visible image has beenfixed, may be removed by swinging back a door 106 which is hinged to theback of the housing. by a hinge 108.

FIGURE 3 illustrates another form of the method of the invention forprinting copies from a permanent image by an electrophotographicprocess. A housing is illustrated at 112 wherein a hollow, cylindricallyshaped or tubular electret 114 is located to rotate about a horizontalaxis. The tubular electret is made of a transparent material such as aclear plastic, glass or the like and the outer surface 118 is coatedwith a photoconductive insulative material. The outer surface 118 of theelectret, beneath the coating 116, and the inner surface 120 are ofopposite polarity and are permanently electrostatically against theinner surface of the electret by means of clips or similar holdingdevices that will retain it against the surface, but which are notshown. As illustrated, the film is held to the inner surface 120 by asheet of clear semirigid plastic 124 which may be supported betweenrigid 1 stops, not shown.

The inside of the tube contains a light source 126 i that location. Alight source can also be placed very near to the inner surface of theelectret at a point where the image transfer to the photoconductivesurface 116 is to take place.

A light shield 128 is provided to restrict the light to the requiredlongitudinal area. As illustrated, the shield 128 has a break or slit130 along one side in order that the light rays may pass therethrough topass through the transparent holder 124; the negative 122,-and theelectret 114.

A grounding brush 132 is provided supported on a holder 134 to be inbrushing contact with the outer photo conductive layer 116. The brushgrounds the outer layer and removes stray charges which would create afalse image.

As the electret tube 114 rotates in a clockwise direction, asillustrated in FIG. 3, the outer photoconductive coating or surface 116passes through a dusting-box 136. The dusting box exposes thephotoconductive surface 116, which has had the latent imagephotoelectrically placed thereon in passing the light exposure of theslit 130, to a fine pigment dust. The dust is attracted to the coating118 in the form and density in accordance with the latent image on thefilm.

As the coated surface 118 carrying the image, made visible by theattracted powder, leaves the dusting box 136 it is engaged by transfercylinder 138 carrying a blanket transfer surface 140. The transfercylinder is geared to the electret cylinder, in a drive not shown, sothat where their surfaces meet at a nip 142 they will have an equalperipheral speed. It should also be understood that the transfercylinder 13-8 and the electret cylinder 114 can be conveniently made ofthe same diameter thereby insuring equal peripheral speeds.

' The blanket or transfer surface on the cylinder, is of a nature thatwill have a greater affinity for the powder or dust on the electretcylinder than the surface 118 of the electret cylinder. The dust willthus be transferred to the surface 140 of transfer cylinder remaining inthe form of the image. The dust or powder, which has been transferred tothe blanket surface 140 by contact and stantially meet. The paper isrolled from a supply roll 148 onto a take-up roll 150.

The electret roll or cylinder 146 has anouter surface 152 exhibiting apermanent electrostatic charge of a polarity opposite that of the outersurface 118 of the electret tube 114. Thus the powder forming thevisible image, which is coated on the surface 140 of the transfer roll,is attracted to the electret roll 146 and coats on the image-receivingpaper 144.

The blanket surface 140 of the transfer cylinder 138 may be coated witha material such as rubber which has a greater afiinity for the powderimage than the insulating surface 116 of the electret tube 114. In oneform it is advisable to ground the surface 116 of the electret toexpedite transfer of the image to the blanket 140. This may beaccomplished by embedding small particles of copper or similar substanceinto the blanket surface .140 of the transfer, cylinder 138.

After the image has been transferred to the paper 144, it is carriedupwardly on the surface of the paper to a fixing element 154 which maybe in the form of a spray or vapor or a heating element. As illustrated,the fixing element 154 provides a heating element 156 which fixes theimage to the paper 144.

In the form shown in FIGURE 4, a hollow electret tube 160 is carriedpartially exposed in a housing 162 to-rotate about a horizontal axis.The electret has an outer surface 163 exhibiting a permanentelectrostatic charge.

In this form of the invention, the film 164 is clamped to the outersurface 163 of the electret cylinder tube 160. The film may be held tothe surface by various means but may be pulled tightly thereto by a thinouter sheet of plastic material 166. This plastic material may be amaterial such as Mylar polyester film which is available commercially.

The thin plastic sheet is clamped to the cylinder at one end drawntightly by appropriate clamps (not shown in detail) at the other end,with the clamped ends being shown generally at 168.

The outer thin material 166 is dipped in a thin solution ofphotoconductive insulating material and is coated thereby.

The light source is shown at 170 and in this form is on the outside ofthe electret tube 160. The light source may be placed within a housing172 having a nan row slit 174 across the front to expose thephotoconduct-ive layer 166 of the film 1 64 to the light across anaxially extending area.

A ground brush 176 is provided carried on a holder 177 to neutralize theouter plastic material and remove stray electrostatic fields therefrom.

When the photoconductive material 166 has been carried past the lightsource, it next passes through a dust chamber 178. In the dust chamber178, the surface of the photoconductive material 166 is exposed to afine dust or pigment which is attracted to the surface in the shape anddensity of the image to be printed.

After the dust chamber, the continued rotation of the electret tube 160exposes the photoconductive material 166 to alight source 180. Thislight source brings a charge to the entire surface.

In the form embodied in FIGURE 4, the transfer roll is omitted and thephotoconductive layer 166 is next pressed against a copy material suchas a paper 182 fed from a supply roll 184 and rolled onto a take-up roll186. The paper passes between the photoconductive layer 166 and a paperelectretroll 188. The paper electret roll has an outer surface 190 whichis opposite in polarity to the outer surface 163 of the electret tube160. This causes an attraction and a transfer of the visible imageformed by the powder on the 'photoconductive material 166 to the paper182.

The image, carried on the paper 182, next passes over the image fixingelement 192. The fixing element may be in the form of a heating element194, as illustrated, or may spray vapor on the surface to fix the powderthereto.

The method is well adapted to use in printing or copying permanentimages and employs simple, easily maintained and simply constructedapparatus. Copies can be continuously and rapidly printed with theadvantages referred to.

Thus, it will be seen that we have provided methods and apparatus forelectrophotographically taking permanent images and printing copiesembodying principles and features of the invention hereinbefore setforth. The features of invention are well adapted to use with a cameraand avoid the necessity of providing the cumbersome and complicateddevices necessary with methods and apparatus heretofore used.

We have, in the drawings and specifications, presented a detaileddisclosure of the preferred embodiments of our invention, but it is tobe understood that we do not intend to limit the invention to thespecific forms disclosed, but

intend to cover all modifications, changes, and alternativeconstructions and methods falling within the scope of the principlestaught by our invention.

We claim as our invention: 7

1. In combination, a camera means for making an image by anelectrophotographic process which comprises a lens, a closed camerachamber exposed to light only through the lens, a shutter system forcontrolling the opening of the lens and exposing the camera chamber toan exterior image for a controlled period of time, an electret withinthe camera chamber having a surface face ing the lens and includingopposed coextensive parallel surfaces each exhibiting permanentlycharged electrostatic fields of opposite polarity, means at one side ofsaid electret supplying an area of image-forming material with aphotoconductive layer thereon md adapted to be placed over theelectrostatically charged surface facing the lens, a movable groundingelement adapted to be moved over the surface of the image-formingmaterial whereby stray charges on the surface thereof are discharged,and means for subjecting the image-forming area to contact withelectrostatically attracted material to form a visible image on thesurface of said image-forming material.

2. An electrophotographic camera combination comprising means forming aclosed lightproof camera chamher, a' lens positioned to expose theinterior of the chamadapted to open the lens for a predetermined periodof time wherein light radiation enters the camera chamber,

a plate of permanently electrically pre-stressed substance havingparallel surfaces exhibiting permanently charged electrostatic fields ofopposite polarity with one of said surfaces facing the light radiationwhich enters the camera chamber through the lens, means for movablysupplying an image-forming strip of material having a photoconductivelayer adjacent a second layer whereby radiation maybe projected throughthe lens onto said photoconductive layer while it is in proximaterelationship to the surface of the electrically stressed plate, astationary ground bar located so that the moving image-forming stripwill pass in close proximity thereto to remove stray electrostaticfields from the photoconductive surface thereof, and means locatedadjacent the electrically pre-stressed plate providing an atmosphere ofelectrostatically attracted material whereby the surface of saidimageforming strip is coated with the material in a shape and densityvarying with the radiation received in accordance with the lightemitting properties of the image, and means for fixing the layer ofelectrostatically attracted material on the image-forming strip torender the image permanent.

3. In a mechanism for producing an image by an electrophotographicprocess comprising a closed lightproof camera chamber, an electret platewithin said chamber having opposed parallel spaced surfaces beingcharged with a permanent strong electrostatic field withroppositesurface having opposite polarity, a lens for said camera chamber locatedso that radiation passing through the lens will engage an area adjacentone surface of the elec: tret, a shutter system for the lens adapted topermit pas-' sensitive pigment particles whereby the particles arecoated on the image-forming material with a shape and density varyingwith the latent image on the surface thereof in accordance with theradiation received, and means for fixing the pigment particles on thesurface of the image-forming material.

4. A camera for making an image by an electrophotographic process Whichcomprises a lightproof camera chamber, a lens and shutter combination atthe front of the chamber adaptedto open the lens for radiation to theback of the chamber in accordance with an image to be reproduced, anelectret plate at the back of the chaml a 9 reproduced, a developingchamber having means for providing an atmosphere of electrostaticresponsive pigment in minute particles which will coat the image-formingstrip with a shape and density in accordance with the radiation receivedthrough the lens, and a second fixing chamber with means to spray acoating of material over the image-forming strip whereby the visibleimage is' fixed on the surface of the image-forming strip.

5. In a photoelectric camera combination, a charging means having anelectret plate having opposing parallel coextensive surfaces eachcharged with a permanent electrostatic field with opposite surfaceshaving opposing polarity, a camera housing supporting said plate andforming a lightproof camera chamber, a lens at one end of the chamberlocated to expose an image forming strip to radiation emitted from animageexternally of the camera, a shutter system for the lens adapted toopen the lens for a predetermined length of time, means with- 4 10conductive insulation layer on the outer surface of the electretelement, means for moving and supporting a film on the inner surface ofthe electret element, a light source Within the tubular electret wherebylight radiation will pass through the film and transparent electret toimpress a latent image on the photoconductive insulation layer, meansfor applying a powdered pigment material to the insulation layer on thesurface which is attached to the layer in accordance with the latentimage thereon, a transthe particles are transferred to the surfacethereof, and

in the housing supplying a strip of image-forming material ofa clearplastic with a photoconductive insulating surface thereon, saidimage-forming material being drawn across the surface of the electretplate, a developing chamber filled with dust particles of pigmentsusceptible to electrostatic attraction whereby the pigment particlesare coated on the image-forming strip with a shape and density dependentupon the radiation received by the image-forming strip, and a fixingchamber adjacent the developing chamber provided with a-coating spraywhereby the pigment particles are adhered to the surface of theimage-forming strip to permanize the image.

6. In an electrophotographic apparatus comprising a camera housingdefining a lightproof camera chamber, a lens member at the front of thechamber for admitting radiation in accordance with the character of animage, a shutter assembly for the lens, a light-reflecting surface atthe back of the camera chamber positioned substantially at an angle of45 with the axis of the lens whereby the'light rays will be reflectedvertically upwardly to an image-receiving position'when the camera ispositioned horizontally, means for movably' supplying a strip ofimage-forming material in theimage-receiving position across the top ofthe camera chamber, said material having a layer of photoconductivematerial thereon, an electret having a surface located for engagementwith the imageforming strip as it is drawn into image-receivingposition, whereby radiation will produce a latent charge image on saidphotoconductive layer, and means for developing and. fixing said latentimage into a permanent image by subjectingthe strip to anelectrostatically attracted dust and by adhering the dust to the stripafter it is accumulated thereon in the shape and density of the latentimage,

7. In an electrophotographic apparatus, an electret member havingopposed surfaces permanently charged with electrostatic fields ofopposite polarity and having coatings of electrically conductivematerial over each of said surfaces, means for passing an image-formingmaterial in effective electrical engagement with the first layer ofelectrically conductive material and subsequently in engagement with thesecond layer of electrically conductive material, means for placing agrounded plate in coextensive juxtaposed relationship with theimage-forming material after it has been passed over the conductivelayers, a camera lens system exposing the photoconductive layer on theimage-forming material to a radiation in accordance with an image to bereproduced, and deveioping and fixing means for permanizing the latentimage on the photoconductive layer by dusting the layer with anelectrostatically attracted powder and adhering the powder in itsattracted positions in densities and shapes varying with the radiationreceived by the material.

'8. A mechanism for reproducing images electrophotographicallycomprising a tubular shaped transparent electret element having innerand outer surfaces permanently charged electrostatically with opposedpolarity, a photomeans for fixing the particles transferred to saidmaterial. 9. A mechanism for reproducing images in accordance with claim8 wherein electrical conductive material is embedded in the surface ofthe transfer cylinder to ground the surface of the electret tube incontact with the transfer cylinder to expedite transfer of the image tothe cylinder.

10. A mechanism for reproducing images electrophotographicallycomprising a transparent electret element having first and secondsurfaces permanently picture charged electrostatically with opposedpolarity, a photoconductive layer on the second surface of the electretelement, a light source located adjacent the first surface whereby lightrays may be projected through a film place againstrthe first surface andthrough the transparent electret to the photoconductive insulationlayer, means for applying a powdered material attracted by the charge onthe insulated surface whereby a visible image will be produced thereondependent on the intensity of the radiated latent image thereon, atransfer blanket means having a greater afiinity for the powderedmaterial than the insulated surface and adapted to remove the powderedmaterial in the charge pattern in which it has formed on the insulatedsurface, a second electret element having a permanently chargedelectrostatic surface with .a polarity opposed to that of said'secondsurface of the transparent electret, whereby the second electret may be.pressed against the transfer means with an image-receiving meansvtherebetween and the powdered material will attract itself to theimage-receiving means in the pattern of the image, and means for fixingthe material to said image-receiving means.

11. A mechanism for rotary printing of images by an electrophotographicprocess which comprises a hollow cylindrically-shaped electret havinginner and outer surfaces with a permanent electrostatic charge ofopposed polarity, means on the inner surface of the electret cylinderfor supporting a film, a light source positioned within the electretcylinder, a light shield having a narrow lightpassing strip extendingaxially across the cylinder and limiting the light passage through thefilm and the electret to the narrow strip, a coating of photoconductiveinsulation material on the outer surface of the electret, means forapplying a material to the outer surface of the cylinder which willafiix itself thereto in the pattern of the image impressed on it by thelight radiation passing through the electret and film, a transfer rollrotatable about an axis parallel to the electret cylinder and having anouter blanket surface with an afiinity for the material attached to thesurface of the electret cylinder to thereby remove said material in thepattern of the image, a second rotatable electret having an outerpermanently charged electrostatic surface with a polarity opposite thatof the outer surface of the electret cylinder, means for passing a stripof image-receiving material between the transfer roll and the secondelectret whereby the image will aifix itself to the material, and meansfor receiving the material from the second electret and operative to fixthe attracted material to the surface for a permanent print.

a bearing means on the. inner surface on the electret element, a lightsource within the tubular electret whereby light radiation will passthrough the image and transparent electret to impress a latent image onthe photo-j conductive insulation layer, means for applying a powderedpigment material to the insulation layer on the surface which isattached to the layer in accordance with the latent image thereon, atransfer cylinder positioned to be rotated about an axis parallel withthe tube and having an outer surface with an affinity for the powderedpigment, a grounding brush positioned in contact with the insulationlayer after contact with the transfer cylindena copy material adapted tobe rolled in engagment with the transfer cylinder whereby the particlesare transferred to the surface thereof, and means for fixing theparticles transferred to said copy material.

13. A mechanism for reproducing images electropho'tographicallycomprising a rotating cylinder forming an electret with the inner andouter surfaces of opposing polarity, means for attaching a thin plasticmaterial with a photoconductive insulating surface thereon to the outerperipheral surface of the cylinder wherein an image-bearing film may beheld between the plastic material and cylinder, a light sourceexteriorly of the cylinder adapted to apply light radiation to thephotoconductive surf-ace of the thin plastic material, a dust chamberfor applying a .pigment dust to the outer surface of the plasticmaterial whereby the latent image is rendered visible, and a secondelectret cylinder having an outer surface permanently electrostaticall-ycharged and being of a polarity opposing the polarity of the outersurface of the first electret cylinder, means for passing a copy paperbetween said cylinders, said paper receiving'the image in its visibleform from the layer of thin plastic material as attracted by the surfaceof the second electret.

14. In combination in a camera for making an image by electrophotographycomprising a closed light-proof camera chamber, a lens located at oneend of the chamber, a shutter device to be opened to expose the interiorof the closed chamber through the lens to an image to be photographed,an electret in said camera having a flat surface facing said lens andpossessing a permanently precharged electric fieldof a given polarity,film advancing and guide means movably positioning strip formimageforming material having a layer of photoconductive material inadjacent coextensive relationship across said flat surface of saidelectret, whereby radiation may be projected into said photoconductivelayer when said lens is opened, and a developing chamber into which saidstrip material is moved away from said electret and having an atmosphereof charge-responsive material coating the image-forming materialnon-uniformly with a shape and density varying with the radiationreceived from the image. I Y

15. An electrophotographic reproduction apparatus which includes, anelectret,.means passing. a layer'of image-forming material having aphotoconductive layer through the permanent electrostatic field adjacentthe surface of the electret, means forming a grounded surface in closeproximity to the image-forming material, camera lens means for exposingthe photoconductive layer of image-forming material to a radiation in animage to be reproduced to form a latent electrostatic image in theimage-forming material, and means for developing the image to render itvisible.

16. An electrophotographic reproduction apparatus including an electret,means passing an image-forming material having a photoconductive layerattached thereto through the "permanent electrostatic field adjacent thesurface of an electret, means passing the image-forming material inelectrical contact with a layer of electrically conductive material on afirst surface of said electret, and subsequently with a second layer ofelectrically conductive material on another surface of said electret,means placing a coextensive ground adjacent the image-forming material,a camera lens system for exposing the imageforming material to aradiation in accordance with an image to be reproduced to formulate anelectrostatic image on the photoconductive layer, and means fordeveloping and fixing the image on the image-forming material. V V g VReferences Cited in the file of this patent UNITED STATES PATENTS2,221,776 I Carlson Nov. 16, 1940 2,297,691 ,Carlson Oct. 6, 19422,543,051 Oughton et a1 Feb. 27, 1951 2,551,582 Carlson May 8, 19512,693,416 Butterfield Nov. 2, 1954 2,695,363 Marvin Nov. 23, 19542,732,775 Young et al. Jan. 31, 1956 2,781,704 Mayo et al. Feb. 19, 19572,831,409 Bixby et al. Apr. 22, 1958 2,843,084 I-Iayford July 15, 1958"OTHER REFERENCES page 470.

Electrical Engineering, October 1953, pages 869-872. I

Radio Electronics, January 1950, pages 8-82.

